There are many different techniques for forming electrical connections on or to substrates and/or burning-in semi-conductor chips mounted on a substrate. One technique utilizes so-called solder balls or solder-pads arranged in a predetermined pattern on a substrate which solder balls in turn are electrically connected to chips or other substrates to form the necessary circuitry. It is desirable, if not necessary, to test the electrical connections or the electrical integrity of these solder balls and their associated circuitry before final assembly of the product to thereby determine if in fact there is any deficient or defective connections. These can either be repaired or if repair is not feasible, the part can be scrapped before any further work is done thereby minimizing any losses. Testing of these solder ball connections has taken various forms. One form is to provide a test fixture having an array of probes either in the form of spring loaded pins or in the form of buckling beams which pins or beams are arrayed in the configuration of the solder balls on the substrate. The pins or beams are supported in a fixture which moves them into and out of contact with the solder balls, and the necessary tests or burn-in procedures can be performed with a pin or beam contacting each solder ball.
This type of test or burn-in connection has several drawbacks and limitations. One of these limitations is that the probe contact is with the highest point on the solder ball. Since this is point-to-point contact with a round portion of the ball, it is sometimes difficult to make good contact thus resulting in occasional false readings or improper burn-in. Additionally, as the spacing between the solder balls becomes closer and closer due to advancing technology, it becomes more and more difficult to provide for pins which are physically arranged and supported and properly mounted within such close confines thereby making testing more difficult. Additionally with the decreasing distance between the solder balls there is an increase in the density of the solder balls on a given surface area thus necessitating a significant increase in the density of the pins for testing; this can increase significantly the cost of test fixtures and increase the possibility of failures due to the increase in number of pins required.